1. Field of the Invention
The present invention relates to a system of computing surface reconstruction, in-plane and out-of-plane displacements and strain distribution on a test surface of a test object before and after the stress is applied.
2. Description of Related Art
The interferometer has been widely used in surface topography measurement, applied to semiconductor wafers, liquid crystal display glass panels in a manner of non-contact measurement. Types of setting an optical path of the interferometer mainly include Mirau, Linnik, and Michelson. References may be made to FIG. 1A, FIG. 1B, and FIG. 1C. FIG. 1A is a schematic architecture of a conventional Mirau type interferometer. FIG. 1B is a schematic architecture of a conventional Linnik type interferometer. FIG. 1C is a schematic architecture of a conventional Michelson type interferometer.
In the Mirau type interferometer 101 and the Michelson type interferometer 103, their reference surfaces and the objective lens are fixed and usually integrated onto their respective objective lens, which means they cannot be adjusted. Most of optical vendors have the Mirau type interferometer 101 and the Michelson type interferometer 103 already. The optical architecture of the Linnik type interferometer 102 has high flexibility in adjusting the reference optical component and is advantageously self-assembled.
Interference principle uses interference waves generated by an optical path difference between the test surface of the test object and reference light to assess optical properties of the test surface of the test object. Furthermore, with the use of an image capture device and a piezoelectric actuator, the topography measurement to the test surface of test object can be achieved, and then applied to size, profile roughness, and defects on the test surface of the test object.
For the interferometer technology, ROC Patent No. I274849, for example, uses the Mirau type interferometer along with the interference peak calculus to improve shortcomings in U.S. Pat. Nos. 5,633,715, 5,133,601, and 5,398,113, such as huge amount of data in computing algorithm for interference wave calculus and significant time consuming, while keeping its measurement accuracy and reducing computing time.
In application, R.O.C. Patent No. I333059 discloses the use of the interferometer to measure the surface profile and the film stress on a hard substrate or flexible substrate. In hardware innovation, R.O.C. Patent No. I245926 discloses an interference scanning device in which every time when in measurement, the measured object should be moved at the same level for obtaining the measurement results along the ascending and descending of the interferometer, increasing the scanning speed and accuracy.
Most of the commercially available interferometers aim at measuring the test surface of the test object. Different multiples of the measurement corresponds to different interference devices. Related patents majorly focus in the calculation of peak positions of the interference waves and the minimization in the amount of hardware in order to reduce the computing time, with good measurement accuracy and competitive computing speed. However the fixed integration in architecture of the hardware of the interferometer limits its applications to other purposes of measurements. Basically, the current related researches are mainly focus on the wave peak calculus of interferograms, rather than the improvement of hardware architecture to development of new applications for measurement.
The principle of digital image measurement is to work out relative locations for every giving a point-set on an image by comparing the correlations with point-sets in other images by means of finding the most likely gray level distribution for example. Due to the improvement of image capture devices and computing speed, the digital image measurement technique has been increased.
R.O.C. Patent Application No. 201 140 494 discloses a digital image correlation which divides captured images into a plurality of smaller sub-regions. Reference can be made to FIG. 2 which is a schematic view of images corresponding to sub-regions before and after deformation of a test object in the prior art.
A sub-region 201 is one of un-deformed sub-regions divided before deformation of the test object. A deformation. A sub-region 202 is one of deformed sub-regions divided after deformation of the test object. In order to increase the comparison effect and analysis accuracy, the test surface of the test object has randomly-produced irregular speckle patterns which show in the sub-region 201 and the sub-region 202.
The image capture device is used to capture images of the test object. With the use of deformation theory and algorithms, the patterns of the test object before and after deformation are compared to obtain the deformed sub-region 202 corresponding to the sub-region 201 before deformation, and the displacement and strain of the deformed sub-region 202. After analysis and computation of all sub-regions, the whole deformation on the test surface of the test object can be obtained.
The digital image measurement technique has two categories: two-dimensional technology and three-dimensional technology. The two-dimensional digital image correlation is to obtain the displacement and deformation data of the test object by comparing two digital images in provision that the distance between the test object to be shot and the capture device needs to be constant for the purpose of getting higher measurement accuracy. If the distance between the test object to be shot and the capture device is not constant, then measurement errors occur and the accuracy will be affected, which will need three-dimensional digital measurement technology.
The principle for the three-dimensional digital image measurement is similar to the principle of human-eyes identifying the location and the distance from a specific object. Identification of the test object in three-dimensional coordinates needs to use two images captured from the test object at two different locations. Correlation between the two images defines the related location for each point on the images and further reads the coordinates in space for the test object. In the well-developed three-dimensional measurement techniques, capturing the images of the test object at two different locations is mostly applied to capture the test object at different angles by using tow image capture devices, and then the two images captured at different angles are used to calculate the three-dimensional coordinates of the test object from the corresponding relationship for each point in the images by using the two-dimensional digital image measurement technology.
R.O.C. Patent Application No. 201 140 494 discloses a three-dimensional image measurement analysis system using three-dimensional digital image correlation (3D-DIC), which has a non-contact and non-destructive characteristics. Reference can be made to FIG. 3 which is a schematic view of architecture of a conventional three-dimensional digital image correlation system.
The architecture of a conventional three-dimensional digital image correlation system includes a first image capture device 301, a second image capture device 302, a light source 303 and a processing device 304. The first image capture device 301 and the second image capture device 302 can be a CCD camera or camcorder.
A test object 305 is set at a lens focal point of the first image capture device 301 and the second image capture device 302. The light source 303 projects uniform light onto the test object 305. The first image capture device 301 and the second image capture device 302 capture the images of the test surface of the test object 305. The captured images are input to the image input processing unit 304 for image data processing and analysis.
However, in the above three-dimensional digital image measurement, the two image capture devices used to capture the images at two different locations may have different mechanical and optical properties, and the related position between the two image capture devices is not constant, resulting in significant error in image calibration and adversely affecting image accuracy. Therefore, it is quite difficult for image calibration in the three-dimensional coordinate measurement in the prior art which uses the two image capture devices.
Please refer to FIG. 4 which is a schematic view of a conventional three-dimensional coordinate measurement. R.O.C. Patent Application No. 201 124 698 discloses a three-dimensional coordinate measurement which measures a test object, based on a three-dimensional digital image measurement device. First, a single image capture device 401 shoots a first image to a test object 402. With the movement of a shifting device (not shown), a relative displacement between the image capture device 401 and the test object 402 generates. Then, the image capture device 401 shoots a second image. The first image and the second image are respectively subject to analysis and computation by a control device (not shown) to obtain the three-dimensional coordinates of the test object 402.
Since shooting the first image and second image is performed at the same mechanical and optical conditions, only one different condition between these two shots is the lateral displacement. Therefore, the parameter calibration can be simplified and the measurement accuracy is increased, which increases convenience in measurement and dynamic measurement effect. However, it needs to move the image capture device 401, or move the test object 402 to generate the relative displacement in order to achieve the measurement of three-dimensional coordinates of the test object.
Therefore, there is a need of a novel means to solve the existing problems such as limitations to integration of configuration, and complexity and errors in parameter calibration due to inherent mechanical and optical properties.